1. Field of the Invention
The present invention relates to a color combining optical element and projection type image display apparatus using it and is suitably applicable, for example, to color liquid crystal projectors for projecting an enlarged image from projection original images based on color liquid crystal panels, onto a screen surface.
Related Background Art
A variety of proposals have been made heretofore for projection apparatus (liquid crystal projectors) constructed to project an enlarged image from projection original images based on liquid crystal light valves, onto the screen surface.
In the projection apparatus of this type, image display elements (liquid crystal panels) based on images of three colors of R, G, and B are illuminated by respective color light beams obtained by color separation of light from a light source. The respective color beams transmitted by the image display elements are guided through a color combining means to be projected through one projection lens onto the screen surface or the like.
Conventionally, a cross dichroic prism is known as one of color combining optical elements used in the liquid crystal projectors. FIG. 5 is a schematic view to show the major part of a projection type image display apparatus using the conventional cross dichroic prism. The cross dichroic prism XDP used in the projection image display apparatus illustrated in FIG. 5 is composed of four rectangular prisms 31, 32, 33, and 34, and dichroic layers DM1, DM2 having two types of reflection wavelength regions cross inside the prism.
In the projection image display apparatus of FIG. 5, a parabolic mirror 2 converts white light emitted from light source 1, into a nearly parallel beam, and a first fly-eye lens 3 consisting of an array of rectangular lenses forms light source images in almost center regions of respective lenses in a second fly-eye lens 4 consisting of an array of rectangular lenses. Then a polarization converting element 5 emits beams of only one polarization component and the beams of one polarization component are laid over image modulating means 16, 18, 20 by a first positive lens 6. Blue light reflected by a blue reflecting dichroic mirror 8 is guided via a light reflecting mirror 9 and a second positive lens 15 to be converged on a display portion of image modulating means 16 for blue. The green component out of green and red components transmitted by the blue reflecting dichroic mirror 8 is reflected by a dichroic mirror 10 for reflecting green, and is guided through a third positive lens 17 to be converged on a display portion of image modulating means 18 for green. The light of the red component transmitted by the dichroic mirror 10 is guided via a fourth positive lens 27, a high reflecting mirror 28, a fifth positive lens 29, a high reflecting mirror 30, and a sixth positive lens 26 to be converged on a display portion of image modulating means 16 for red.
Light beams modulated by the respective color image modulating means 16, 18, 20 undergo color composition in the cross dichroic prism XDP composed of the first prism 31, second prism 32, third prism 33, and fourth prism 34, to be projected as a color image onto the screen not shown, by a projection lens 35.
Unless the cross dichroic prism as a color combining prism illustrated in FIG. 5 is made by accurately forming the angles of the four rectangular prisms and polishing each of the surfaces thereof, the dichroic layers DM1, DM2 will be bent at the apexes of the rectangular prisms.
This caused the problem that the projected image appeared double on the unrepresented screen and thus resolution sensation became considerably poor. In order to keep good resolution on the screen, the four rectangular prisms 31, 32, 33, 34 had to be joined without a level difference at their joint surfaces, and thus close attention had to be paid for the joining work. The right-angled ridge portions of the rectangular prisms had to be made without any such defects as kinks, chips, or the like, and if the width of the ridge portions was too wide there arose the problem that the cross part of the cross prism was projected as a vertical stripe on the screen. As described, the conventional cross dichroic prism was made by the extremely difficult prism processing and prism joining works and thus required considerable time and expenditure for manufacturing.
On the other hand, in order to avoid the above-stated problems of the cross dichroic prism, Japanese Patent Application Laid-Open No. 10-104763 describes the proposal of a liquid crystal projector using a color separation prism consisting of three prisms, which has been used as a color separation means in video cameras and the like. However, since the shape of the color separation prism in this application was not optimized so as to minimize the optical path length of the prism, it necessitated the prism path length close to double that of the cross dichroic prism of FIG. 7A, as illustrated in FIG. 8A.
Since the specification of the above application describes nothing about the material and refractive index of the prism, it is not clear whether the air-reduced path length is reduced by increasing the refractive index of the prism.
In the proposal of the above application, as described above, the manufacturing of the prism itself was easier than that of the cross-dichroic prism, but, because of the large size of the prism and the long path length of the prism, the back focus of the projection lens had to be set considerably longer than that in the case of use of the cross dichroic prism. For this reason, the projection lens became large in size and, as to the optical performance of the projection lens, there arose the problem of increase in chromatic aberration of magnification in particular.
An object of the present invention is to propose a compact color combining optical element and a compact color separation optical element shorter in the optical path length and easier to make up than the prism of the above application and provide projection type image display apparatus using the color combining optical element and color separation optical element.
A color combining optical element according to one aspect of the present invention is a color combining optical element comprising three or more prisms, which has a prism comprising a common surface as a surface serving as a total reflection surface and as a transmissive surface on the extreme exit side and which has two dichroic mirror layers for reflecting light of mutually different wavelength regions, wherein the two dichroic mirror layers are located so as not to cross each other, an outline of a cross section of a prism placed between the two dichroic mirror layers, cut by a plane along a color composition direction, is comprised of four or more segments, and at least one of flection points in the cross section of surfaces without the dichroic mirror layers is present at an inner position of the color separation optical element with respect to a segment connecting two ends of segments in the cross section of surfaces with the two dichroic mirror layers.
A color combining optical element according to a further aspect of the invention is a color combining optical element comprising three or more prisms, which has a prism comprising a common surface as a surface serving as a total reflection surface and as a transmissive surface on the extreme exit side and which has two dichroic mirror layers for reflecting light of mutually different wavelength regions, wherein the two dichroic mirror layers are located so as not to cross each other, an outline of a cross section of a prism placed between the two dichroic mirror layers, cut by a plane along a color composition direction, is comprised of four or more segments, and at least one of interior angles in the outline of the cross section is an angle exceeding 180xc2x0.
A color combining optical element according to a still further aspect of the invention is a color combining optical element comprising four or more prisms, which has a prism comprising a common surface as a surface serving as a total reflection surface and as a transmissive surface on the extreme exit side and which has two dichroic mirror layers for reflecting light of mutually different wavelength regions, wherein the two dichroic mirror layers are located so as not to cross each other, and wherein a plurality of prisms are placed between the two dichroic mirror layers.
A color combining optical element according to a still further aspect of the invention is a color combining optical element comprising: in the order named hereinafter from the light exit side, a first prism comprising three or more optically smooth surfaces, among which one surface comprises a common surface as a surface serving as a transmissive surface and as a total reflection surface; a second prism comprising two or more optically smooth surfaces; a third prism comprising three or more optically smooth surfaces; and a fourth prism comprising two or more optically smooth surfaces, wherein a dichroic mirror layer for reflecting first color light is provided on one or both of opposed surfaces of the first prism and the second prism and a dichroic mirror layer for reflecting second color light on one or both of opposed surfaces of the third prism and the fourth prism.
In one aspect of the above color combining optical element, the first prism and the second prism are joined with each other with said dichroic mirror layer in between and the third prism and the fourth prism are joined with each other with said dichroic mirror layer in between.
In another aspect of the above color combining optical element, the second prism and the third prism are joined with each other.
In another aspect of the above color combining optical elements, an angle xcex81 between a surface with the dichroic mirror layer on the exit side and said common surface, satisfies the following condition:
20xc2x0 less than xcex81 less than 35xc2x0. 
In another aspect of the above color combining optical elements, an angle xcex82 between said common surface and a surface with the dichroic mirror layer on the entrance side out of said two dichroic mirror layers, satisfies the following condition:
40xc2x0 less than xcex82 less than 50xc2x0. 
In another aspect of the above color combining optical elements, a refractive index Nd for d-line of a material of said prisms satisfies the following condition:
1.56 less than Nd. 
In another aspect of the above color combining optical elements, an Abbe""s number xcexdd of a material of said prisms satisfies the following condition:
40 less than xcexdd. 
In another aspect of the above color combining optical element, each of said third prism and said fourth prism is comprised of a right triangular prism having apex angles of 45xc2x0.
In another aspect of the above color combining optical element, said third prism and fourth prism are integrally formed with each other.
A color combining optical element according to another aspect of the invention is a color combining optical element comprising three or more prisms, wherein one of the three prisms has a prism comprising a surface serving as a total reflection surface and as a transmissive surface on the extreme exit side, the optical element has two dichroic mirror layers for reflecting color light of two types of different wavelength regions, the two dichroic mirror layers are located so as not to cross each other, and wherein when xcex81 represents an angle between the common surface and the exit-side dichroic mirror layer and xcex82 an angle between the common surface and the entrance-side dichroic mirror layer, the angles xcex81 and xcex82 satisfy the following conditions:
20xc2x0 less than xcex81 less than 35xc2x0, and 
40xc2x0 less than xcex82 less than 50xc2x0. 
In another aspect of the above color combining optical element, when Nd represents a refractive index for d-line of a material of said prisms and xcexdd an Abbe""s number of the material of the prisms, Nd and xcexdd satisfy the following conditions:
1.56 less than Nd, and 
40 less than xcexdd. 
A color combining optical element according to still another aspect of the invention is a color combining optical element comprising: in the order named hereinafter from the light exit side, a first prism comprising three or more surfaces, among which one surface comprises a surface serving as a transmissive surface and as a total reflection surface; a second prism comprising two or more surfaces; a third prism comprising three or more surfaces; and a fourth prism comprising two or more surfaces, wherein a dichroic mirror layer for reflecting first color light is provided on one or both of opposed surfaces of the first prism and the second prism, a dichroic mirror layer for reflecting second color light on one or both of opposed surfaces of the third prism and the fourth prism, and each of the third prism and the fourth prism is comprised of a right triangular prism having apex angles of 45xc2x0.
In another aspect of the above color combining optical element, when xcex81 represents an angle between said common surface and the exit-side dichroic mirror layer out of said two dichroic mirror layers and xcex82 an angle between the common surface and the entrance-side dichroic mirror layer, the angles xcex81 and xcex82 satisfy the following conditions:
20xc2x0 less than xcex81 less than 35xc2x0, and 
40xc2x0 less than xcex82 less than 50xc2x0. 
In another aspect of the above color combining optical elements, when xcex81 represents an angle between said common surface and the exit-side dichroic mirror layer out of said two dichroic mirror layers and Nd a refractive index for d-line of a material of said prisms, xcex81 and Nd satisfy the following conditions:
20xc2x0 less than xcex81 less than 35xc2x0, and 
1.56 less than Nd. 
In another aspect of the above color combining optical elements, the dichroic mirror layer farther from the exit side out of said two dichroic mirror layers is in contact with each of light incidence surfaces into two prisms in contact with said dichroic mirror layer.
A projection type display apparatus according to one aspect of the invention is a projection type image display apparatus comprising either one of the color combining optical elements described above.
A projection type image display apparatus according to another aspect of the invention is a projection type image display apparatus comprising light generating means for emitting light including color components of the three primary colors, color separation means for separating the light emitted from the light generating means, into three primary color light beams, three image modulating means for receiving the three primary color light beams and modulating the primary color light beams to form optical images, color combining means for composing one composite beam from output light beams from the three image modulating means, and projection means for projecting the composite light beam composed by the color combining means, wherein said color combining means is comprised of either one of the color combining optical elements described above.
A color separation optical element according to one aspect of the invention is a color separation optical element comprising three or more prisms, which has a prism having a common surface as a surface serving as a total reflection surface and as a transmissive surface on the extreme entrance side and which has two dichroic mirror layers for reflecting light of mutually different wavelength regions, wherein the two dichroic mirror layers are located so as not to cross each other, an outline of a cross section of a prism placed between the two dichroic mirror layers, cut by a plane along a color separation direction, is comprised of four or more segments, and at least one of flection points in the cross section of surfaces without the dichroic mirror layers is present at an inner position of the color separation optical element with respect to a segment connecting two ends of segments in the cross section of surfaces with the two dichroic mirror layers.
A color separation optical element according to another aspect of the invention is a color separation optical element comprising three or more prisms, which has a prism comprising a common surface as a surface serving as a total reflection surface and as a transmissive surface on the extreme entrance side and which has two dichroic mirror layers for reflecting light of mutually different wavelength regions, wherein the two dichroic mirror layers are located so as not to cross each other, an outline of a cross section of a prism placed between the two dichroic mirror layers, cut by a plane along a color separation direction, is comprised of four or more segments, and at least one of interior angles in the outline of the cross section is an angle exceeding 180xc2x0.
A color separation optical element according to still another aspect of the invention is a color separation optical element comprising four or more prisms, which has a prism comprising a common surface as a surface serving as a total reflection surface and as a transmissive surface on the extreme entrance side and which has two dichroic mirror layers for reflecting light of mutually different wavelength regions, wherein the two dichroic mirror layers are located so as not to cross each other, and wherein a plurality of prisms are placed between the two dichroic mirror layers.
A color separation optical element according to still another aspect of the invention is a color separation optical element comprising: in the order named hereinafter from the light entrance side, a first prism comprising three or more optically smooth surfaces, among which one surface comprises a common surface serving as a transmissive surface and as a total reflection surface; a second prism comprising two or more optically smooth surfaces; a third prism comprising three or more optically smooth surfaces; and a fourth prism comprising two or more optically smooth surfaces, wherein a dichroic mirror layer for reflecting first color light is provided on one or both of opposed surfaces of the first prism and the second prism and a dichroic mirror layer for reflecting second color light on one or both of opposed surfaces of the third prism and the fourth prism.
In another aspect of the above color separation optical element, the first prism and the second prism are joined with each other with said dichroic mirror layer in between and the third prism and the fourth prism are joined with each other with said dichroic mirror layer in between.
In another aspect of the above color separation optical element, the second prism and the third prism are joined with each other.
In another aspect of the above color separation optical elements, an angle xcex81 between a surface with the dichroic mirror layer on the entrance side and said common surface, satisfies the following condition:
20xc2x0 less than xcex81 less than 35xc2x0. 
In another aspect of the above color separation optical elements, an angle xcex82 between said common surface and the exit-side dichromic mirror layer, satisfies the following condition:
40xc2x0 less than xcex82 less than 50xc2x0. 
In another aspect of the above color separation optical elements, a refractive index Nd for d-line of a material of said prisms satisfies the following condition:
1.56 less than Nd. 
In another aspect of the above color separation optical elements, an Abbe""s number xcexdd of a material of said prisms satisfies the following condition:
40 less than xcexdd. 
In another aspect of the above color separation optical element, each of said third prism and said fourth prism is comprised of a right triangular prism having apex angles of 45xc2x0.
In another aspect of the above color separation optical element, said third prism and fourth prism are integrally formed with each other.
A color separation optical element according to another aspect of the invention is a color separation optical element comprising three or more prisms, wherein one of the three prisms has a prism comprising a surface serving as a total reflection surface and as a transmissive surface on the extreme entrance side, the optical element has two dichroic mirror layers for reflecting color light of two types of different wavelength regions, the two dichroic mirror layers are located so as not to cross each other, and wherein when xcex81 represents an angle between the common surface and the entrance-side dichroic mirror layer and xcex82 an angle between the common surface and the exit-side dichroic mirror layer, the angles xcex81 and xcex82 satisfy the following conditions:
20xc2x0 less than xcex81 less than 35xc2x0, and 
40xc2x0 less than xcex82 less than 50xc2x0. 
In another aspect of the above color separation optical element, when Nd represents a refractive index for d-line of a material of said prisms and xcexdd an Abbe""s number of the material of the prisms, Nd and xcexdd satisfy the following conditions:
1.56 less than Nd, and 
40 less than xcexdd. 
A color separation optical element according to another aspect of the invention is a color separation optical element comprising: in the order named hereinafter from the light entrance side, a first prism comprising three or more surfaces, among which one surface comprises a surface serving as a transmissive surface and as a total reflection surface; a second prism comprising two or more surfaces; a third prism comprising three or more surfaces; and a fourth prism comprising two or more surfaces, wherein a dichroic mirror layer for reflecting first color light is provided on one or both of opposed surfaces of the first prism and the second prism, a dichroic mirror layer for reflecting second color light on one or both of opposed surfaces of the third prism and the fourth prism, and each of the third prism and the fourth prism is comprised of a right triangular prism having apex angles of 45xc2x0.
In another aspect of the above color separation optical elements, when xcex81 represents an angle between said common surface and the entrance-side dichroic mirror layer and xcex82 an angle between the common surface and the exit-side dichroic mirror layer, the angles xcex81 and xcex82 satisfy the following conditions:
20xc2x0 less than xcex81 less than 35xc2x0, and 
40xc2x0 less than xcex82 less than 50xc2x0. 
In another aspect of the above color separation optical elements, when xcex81 represents an angle between said common surface and the entrance-side dichroic mirror layer out of said two dichroic mirror layers and Nd a refractive index for d-line of a material of said prisms, xcex81 and Nd satisfy the following conditions:
20xc2x0 less than xcex81 less than 35xc2x0, and 
1.56 less than Nd. 
In another aspect of the above color separation optical elements, the dichroic mirror layer farther from the entrance side out of said two dichroic mirror layers is in contact with each of light incidence surfaces into two prisms in contact with said dichroic mirror layer.
A projection type image display apparatus according to another aspect of the invention comprises either one of the color separation optical elements described above.
A projection type image display apparatus according to another aspect of the invention is a projection type image display apparatus comprising light generating means for emitting light including color components of the three primary colors, color separation means for separating the light emitted from the light generating means, into three primary color light beams, three image modulating means for receiving the three primary color light beams and modulating the primary color light beams to form optical images, color combining means for composing one composite beam from the output light beams from the three image modulating means, and projection means for projecting the composite light beam composed by the color combining means, wherein said color separation means is comprised of either one of the color separation optical elements described above.